1. Field of the Invention
This invention relates to organosilicon treatment of TiO.sub.2 particles coated with alumina or alumina-silica having a fluoride compound or fluoride ions associated with them. More particularly, it relates to the improvement in properties such as photostability and humidity resistance of the coated TiO.sub.2 particles by the addition of an organosilicon compound.
2. Description of the Related Art
"Aging" is an effect of environment and occurs as TiO.sub.2 pigment is exposed to high humidity and high temperature. As a result, the TiO.sub.2 tends to agglomerate and there is a loss of optical properties of the TiO.sub.2 pigment when incorporated into powder coatings and plastics applications.
Japanese Patent Application No. SHO 57-163604 discloses a toner composition containing TiO.sub.2 treated with hexyltrimethoxysilane or octyltrimethoxysilane in a toner matrix containing colorant and a fixing component. Therein, the toner exhibits enhanced developing properties, storage properties and longer service life by improving the fluidity of the toner. No mention is made of TiO.sub.2 particles coated with fluoride densifted alumina. Further, no mention is made on improving photostability or improving optical properties.
U.S. Pat. No. 4,460,655 discloses a pigment of TiO.sub.2 particles coated with alumina or alumina-silica and having a fluoride compound or fluoride ions associated with them. The pigment of the invention is highly resistant to discoloration on exposure to ultraviolet light, and, when used in making a paper laminate, gives a product with significantly better lightfastness than one using conventional TiO.sub.2 pigment. Nonetheless, properties such as improved photostability and humidity resistance of the TiO.sub.2 pigment therein can be further enhanced.
Each of the prior art compositions and processes suffers from various deficiencies, and further improvements are desirable.